1. Field of the Invention
The present invention generally relates to a steering process which allows long vehicles to make sharp turns. More specifically, the present invention pertains to a rear wheel steering process for long vehicles, including among others, trucks, busses, stretch limos, and semi-tractors and trailers, enabling their vehicles to safely and easily clear the curb when making sharp turns on narrow city streets.
2. Description of the Related Art
Presently, long vehicle turns in tight situations can be quite dangerous. For example, when turning from one city street to another, the driver of a large trailer rig must begin the turn in the second lane over from the curb, thus taking up both lanes of traffic, in an effort to prevent the rear tandem wheels of the rig from running over the curb and perhaps up on the sidewalk. Similarly, long vehicle turns across four lane intersections can be dangerous. If the trailer is crossing a four lane road, it may take two lanes into the intersection, and take two lanes as it turns.
If the semi is pulling two trailers, the above problem is compounded. In such a situation, the semi turns into the intersection, the first trailer cuts across the curb, and the second trailer crosses on the sidewalk. Long trucks, busses and stretch limos, like the trailers, also must take more than their share of the road when turning sharp corners.
There have been several attempts to overcome the above disadvantages. Some long ladder fire trucks and ladder trailers have a seat and steering wheel over the rear wheels, and a fireman steers the back wheels so as to miss the curb. Steering the back wheels of a vehicle is old art. An early automobile had both front and back wheels that were steerable. Yet, directly steering the rear wheels of a vehicle has its share of problems as well, including the need of an additional driver, just to name one.
It would be beneficial to provide a rear wheel steering system that a single driver can operate by the push of a button. Such a system would improve truck hauling safety. In view of the prior art it can be seen that there is a need for a modified rear wheel steering system for long vehicles. It is to the provision of such a system that the present invention is primarily directed.
The present invention is a rear wheel steering process that enables a long vehicle to make tighter turns than are possible with conventional steering assemblies. The present rear wheel steering system requires only minimal intervention by the driver, and allows the trailer-rig, truck or bus to make sharp turns without crossing into the other lane, yet providing for the rear wheels to miss the curb.
The present rear wheel steering process comprises a control system and a rear wheel guidance system. The control system is capable of automating the steering process of the rear wheels, while the rear wheel guidance system is capable of defining the path for the rear wheels to follow. Preferably, the rear wheel guidance system comprises a guide control wheel that lowers to the travel surface in response to the control system. The rear wheel guidance system can further comprise a gyrocompass assembly housed on a pivotal rear wheel unit.
The description of the present invention will include specific references to a tractor-trailer vehicle type, but it will be understood that the steering system is useful in all manner of vehicle types that incorporate rear wheel assemblies.
Further, the term xe2x80x9ccenterlinexe2x80x9d will be used in references with the vehicle and the wheels of the vehicle, and will be understood to mean as described below. The term xe2x80x9cvehicle lengthwise centerlinexe2x80x9d will refer to the centerline of the vehicle in its direction of travel. For example, when describing a semi, the tractor-trailer lengthwise centerline will be the centerline running between the front and back ends, from the cab to the end of the trailer.
Similarly, the centerline of a particular wheel of the vehicle will refer to the centerline of the wheel in its direction of travel. Thus, for example, in a xe2x80x9cnormal driving statexe2x80x9d, wherein the semi is traveling general straight down the road, the tractor-trailer lengthwise centerline, and all the centerlines of the wheels, would be in generally parallel orientations. It will be understood that if a particular wheel of the vehicle is pivotally enabled on the vehicle, the centerlines of the vehicle and wheel may not always be generally parallel. For example, in a turn (or xe2x80x9cturning statexe2x80x9d), the centerline of the vehicle may rotate out of alignment from the centerline of the pivotal wheel. If the rear wheel(s) of a vehicle were pivotal, and the front wheel(s) of the vehicle were to initiate a turn of the vehicle, while the centerline of the vehicle rotated along the radius of the turn, the rear wheel, free to pivot, might continue to travel in the direction of the vehicle before the turn, because of surface friction, before the rear wheel would rotate into the turn.
Likewise, the xe2x80x9crear wheel unit centerlinexe2x80x9d may, or may not, lie on the lengthwise centerline of the cab. During normal hauling, the centerlines would lie on atop the other. But when the rear wheel unit pivots relative to the length of the trailer, the rear wheel unit lengthwise centerline will similarly angle away from the trailer""s lengthwise centerline.
The present steering system has a xe2x80x9cnormal driving statexe2x80x9d and a xe2x80x9cturning statexe2x80x9d. In the normal driving state, the rear wheels are locked in alignment with the vehicle""s centerline, like any standard trailer. The normal driving state is the typical highway hauling use of the vehicle. As the long vehicle approaches a sharp turn, the driver of the vehicle activates the control system of the rear wheel steering system from the normal driving state to the turning state, wherein the rear wheels are then steerable.
Preferably, the invention is a process of rear wheel steering for a vehicle traveling on a driving surface comprising the steps of resisting the rear wheels from pivoting during the normal driving state so the centerline of the rear wheel remains generally parallel to the centerline of the front wheel. In this way, during highway driving, for example, the rear wheels of the semi can be locked from free pivot. Upon initiation of a turn, the invention maintains the rear wheels in a straight line of travel, although the vehicle has begun to turn on its front wheels. This step of the invention comprises guiding the pivoting of the rear wheel upon entrance of the turning state, and preferably includes the lowering of a guide control wheel. At a preset condition, the rear wheels are then freed from guidance prior to exit of the turning state, so the rear wheels may now pivot, and the vehicle complete the turn.
The control system of the present invention determines when to initiate the step of guiding the pivoting of the rear wheel, and preferably when to initiate the step of freeing the rear wheel from guidance.
The rear wheel(s) of the vehicle may be located on a rear wheel unit. The pivotal rear wheel unit enables the rear wheels to turn through a turning angle about the lengthwise centerline of the vehicle. In city driving applications, the wheels may be powered by fluid cylinders, electric motors or other standard means.
While the vehicle is on the straight highway, the system is in the normal driving state, and the present system is deactivated. The driver can then activate the system via the control system when entering a turn. Upon activation of the present system, the rear wheel guidance system will lower a guide control wheel to safely keep the rear wheels in alignment as the trailer makes its turn down the side street.
If the tandem rear wheel unit is free to pivot on the trailer, it will guide itself straight down the road, without any other means of guidance. However, one cannot safely steer the wheels in this manner. The reason is that if one set of the tandem""s wheels are on dry pavement and the other set is on a wet road or ice and the brakes lock, the wheel unit will always turn crosswise of the road and wreck the trailer. The same thing happens if the brake adjustment on one side is different to that on the other side and the brakes lock on one side. If the rear tandem wheels are free to pivot, they can easily be turned by potholes, blowouts, trash or a minor accident.
The guide control wheel offers the required resistance to pivoting because in order for the rear wheels to pivot, the control wheel would need to slide sideways (perpendicular to wheel travel) on the pavement, and a lever arm between the guide wheel and the pivoted rear wheel unit is long. This resistance to sliding on dry pavement is what keeps rubber tire vehicles moving in the direction the wheels are pointing, and allows precise control of the modern rubber-tired automobiles and trucks on our high speed highways.
Another means of rear wheel guidance uses a gyrocompass which is mounted on the rear wheel unit, and when the rear wheel unit is unlocked from the conventional highway hauling non-pivotable position, the gyroscope is energized, and by means of its controls, keeps the rear wheels rolling straight down the road as the semi turns.
The gyrocompass assembly is a two degree of freedom stable platform having a gyroscope (or xe2x80x9cgyroxe2x80x9d) supported in gimbal rings. The gyroscope is rotatable about a vertical axis. The centerline of the gyro is normally maintained in alignment with the trailer""s lengthwise centerline by biasing elements of the gyrocompass assembly, but once energized, the gyro can resist turning with a force greater than that of the biasing elements. The biasing elements can be springs.
When the semi begins to turn, the trailer also begins to turn, and the rear wheels of the trailer are subjected to a turning force. Yet, the gyro still points as it did when it started (aligned in the lengthwise centerline of the vehicle), so when the trailer turns the trailer frame presses against a gyro frame of the gyrocompass assembly. Upon such contact, a switch to a solenoid valve closes, which operates a turning mechanism that keeps the wheel centerline parallel to the gyroscope centerline.
The turning mechanism can comprise at least one cylinder. For example, when the switch is activated, one of two hydraulic cylinders begins to extend. As the cylinder is attached at one end to the trailer and the other end to the rear wheel unit, when the cylinder begins to extend, it pushes (or pulls) the unit about the pivot, to relieve the contact between the trailer frame and the gyro frame. This maintains the rear tandem wheels in alignment now with the gyro""s centerline, as opposed to the trailer""s centerline.
When the semi enters the intersection and turns down the cross street, the front of the trailer turns at an angle to the semi. However, the rear wheels of the trailer do not turn with the trailer but roll straight down the road guided by the guide control wheel. As the semi continues down the cross street, the turning angle between the lengthwise centerline of the trailer and the centerline of the rear wheels becomes increasing larger, until a preset turning angle is reached, opening a switch of the control system. The rear wheels are then brought back into alignment with the trailer""s centerline with aid of the gyrocompass assembly.
The rear wheels of very long trailers are provided with a turning angle of approximately 45 degrees. This means that about one-half of the trailer has moved into the cross street before the rear of the trailer starts to turn. The wheels thus easily miss the curb, but the body of the trailer might overlap, unless the curb is rounded off.
The turning angle that the wheels can pivot on long, self powered equipment like trucks, busses, and automobiles might be limited by the drive shaft angle, but the turn can be shortened by having a maximum turning angle of approximately 30 degrees. The turn of the rear wheels does not start until the maximum turning angle is reached, and then they would need to turn only (90xe2x88x9230=60) degrees more. A standard front wheel drive set of wheels would allow a greater angle and still take a standard drive shaft.
When the trailer or truck is fully in the cross street and the wheels have realigned with the vehicle""s centerline, they are locked in position for highway hauling.
The control system can be adjusted to allow the driver some control over the angle the wheels can turn and the time to return. For example, the rear trailer wheels can be guided straight ahead to the intersection by the guide control wheel. The rear wheels of the trailer continue to roll straight towards the intersection. When the trailer has turned through an angle to the rear wheels of, for example, 45 degrees, it hits a stop on the tandem wheel unit and can not further turn. The trailer""s wheels remain at this angle, so that the rear of the trailer moves the rest of the way into the intersection at the angle of the wheels. As the rig comes into alignment, the driver switches the controls back to the normal driving position.
For normal sized trailers, trucks, busses and the like, the rear wheels may be returned to the centerline automatically. But for very long vehicles, or two trailers in line, it would be best to let the trailer continue into the intersection at the maximum turning angle of the wheels.
Before the steering system of the present invention, there were few very long trucks, busses or fire engines, but once it is known that such vehicles can make sharp turns if they have the present rear wheel steering system, they may become more widespread.